As someone with ADHD, I will say that you can have unlimited will power and it still might not be enough. You might have the best intentions to get something done and somehow, despite your best efforts, it just doesn't get done. The day slips by and before you know it, the deadline has passed. I've been there way too many times. It's not for lack of trying. Will power helps, but sometimes it only goes so far.

Medication and other remedies make it easier to focus on learning how to manage your symptoms and acquiring habits to help (such as learning how to use a planner), but in the end, you still have to learn the skill, which requires effort.